The present invention relates generally to three-phase alternating current (AC) electrical machines or motors and, more particularly, to a system and method for detecting, localizing and quantifying stator winding faults in such electrical machines.
In industrial facilities, electrical machines such as generators, AC motors, and/or transformers are used in various applications. As one example, induction motors are used for applications like pumping, cooling, material movement, and other applications where cost-efficient and robust motors are required. An electrical distribution system is used in conjunction with electrical machines in such applications, with the electrical distribution system including protection and control components such as breakers, contactors, starters, etc.
In a three-phase system having an electrical distribution system and an AC electrical machine, it is recognized that various factors can lead to three-phase voltage asymmetry/imbalance in the system. That is, both high resistance connections and stator winding faults (stator winding fault) alter the resistance in the system, thereby leading to the three-phase voltage asymmetry/imbalance.
With respect to the high resistance connections in the system, improper connection of protection and/or control components (e.g., when electrical connections become loose or have less wire binding force) can cause high resistance connections to develop in the circuit and accordingly cause excess voltage drops (EVDs) to occur in the distribution circuit. These EVDs can lead to abnormal power dissipation at the connections and correspondingly to over-heated contacts or hot spots in the connections that can initiate fire and equipment damage. Even at an early stage, the voltage drops lead to energy losses as line drops, in effect reducing motor efficiency and motor life for example.
With respect to the stator winding faults in the system, these faults may be caused by the gradual deterioration of winding insulation due to a combination of electromechanical-force-induced vibration, high dv/dt voltage surges, thermal overload, and/or contamination. If a stator winding fault occurs and the windings of the stator are shorted, a large circulating fault current is induced in the shorted turn, leading to localized thermal overloading. This localized thermal overloading can eventually result in motor breakdown due to ground-fault/phase-to-phase-insulation or open-circuit failure within a short period of time, if left undetected.
In light of the above, it is desirable to detect high resistance connections and stator winding faults in an efficient and cost effective manner, so as to identify improper electrical connections in the circuit and faults in the stator winding. However, it is recognized that some existing sensor-less techniques developed for detecting both high resistance connections and stator winding faults rely on a main approach/concept of monitoring the influence of the “change” in the asymmetry of the three-phase system, since the faults occur in one of the phases. Therefore, these sensor-less techniques are based on similar indicators such as the negative-sequence current, relative angle between phases, etc., such that distinguishing between the types of faults can be difficult. Such distinguishing between the two faults, however, is desirable as it allows maintenance to be performed in a more flexible and efficient manner, since the course of action can be determined depending on the type and severity of the fault and the application.
It would therefore be desirable to provide a system and method that is capable of detecting an imbalance in a three-phase voltage and differentiating between such an imbalance being caused by a high resistance connection or a stator winding fault. It would also be desirable for such a system and method to localize a detected high resistance connection/stator winding fault to a particular phase or phases of the distribution circuit and quantify the voltage drop or voltage gain associated with the fault.